The invention is concerned with an adjusting device for moving a moveable part into various positions with a spindle drive which is driven by a servomotor and comprises of a spindle having an external thread and of a sleeve part which surrounds said spindle and has an internal thread in engagement with the external thread.
Adjusting devices of this type are used with an electric servomotor in order, for example, to adjust a side ventilator window of a motor vehicle. An adjusting device of this type is disclosed, for example in U.S. Pat. No. 4,186,524. Side ventilator windows of this type are usually coupled to the chassis in a hinged manner in the region of the B-pillar of the motor vehicle and can be brought by the adjusting device from their closed position via intermediate positions into the open position. It is furthermore already known to arrange the servomotor and the spindle drive directly in the region of the moveable part. However, in the case of ventilator windows it has become apparent that even with a very small thread play between the two threads of below 0.1 mm, noise is produced when driving over bad stretches of road with the ventilator window partially open. Particularly in the case of the rear side ventilator windows of motor vehicles these noises are perceived as being particularly annoying because they arise in the vicinity of the occupants"" heads.
Further reduction in the thread play is not practical because of the accompanying increase in manufacturing costs.
The object of the invention is to provide an adjusting device which reduces the tendency to vibrate and therefore reduces the noise being produced.
According to the invention, the object is achieved by an adjusting device of the type described at the beginning, in which one of the two threads consists of two separate threaded parts, and an elastically prestressable element is provided with whose aid an axial force can be produced between the two threaded parts.
In the solution according to the invention, the axial force built up between the two threaded parts with the aid of the elastically prestressable element is supported via the turns of the thread which is in engagement with these two threaded parts. Under the action of the elastically prestressable element on the threaded parts, which can move axially with respect to each other, the thread play is eliminated under certain axial bearing forces of the two threaded parts in a respectively opposite direction. The play-free engagement of the threaded parts with the other thread of the spindle drive stabilizes the moveable part which is to be adjusted, even when there are relatively strong interfering forces which act from outside and may cause vibrations, for example in the case of side ventilator windows of motor vehicles, if the spindle drive is affected by play. With an adjusting device according to the invention, rattling of a partially open side ventilator window need not be feared, even when driving along bad stretches of road.
Although the increased friction of the spindle drive makes a slightly increased torque necessary in order to adjust the moveable part, said torque can be produced by the servomotor without any problems. The friction can also be influenced in a specific manner by the selection of the elastic element or the size of the prestressing force and can be adapted to the particular requirements.
The adjusting device according to the invention furthermore shows the positive side effect that the modulating noise during movement of the moveable part is clearly reduced.
The elastically prestressable element preferably sits between the two threaded parts. Compared to previous solutions, in this structurally particularly simple solution only one further threaded part and the elastically prestressable element are required, and the additional costs can thus be kept low. In a further preferred refinement of the invention, the elastically prestressable element is compressed, so that a tensionable connection between the threaded parts and the elastic element is not required. However, it would in principle also be conceivable to provide tensioned elastic elements, since it is ultimately immaterial as to whether the thread play is eliminated by the two threaded parts being contracted or pressed apart in the axial direction.
In a particularly simple embodiment of the invention, an O-ring or similar spring element made of elastically flexible material is provided as the elastically prestressable element. An O-ring of this type has the further advantage of only taking up very little axial space, and the spindle drive can therefore be kept short.
In a preferred development of the invention, provision is made for the internal thread to be divided, a first threaded part being connected fixedly to the sleeve and the second threaded part being held in an axially moveable manner with respect to said first threaded part. In such an embodiment, only very few changes are necessary in the region of the spindle drive, in comparison with the previous solutions. For example, the second threaded part can principally consist of a commercially available nut. The second threaded part can expediently be secured to the sleeve at at least one point in the circumferential direction in order to maintain a uniform axial force between the threaded parts constantly during operation. An increase in the number of possible relative angular positions between the second threaded part and the sleeve is advantageous, particularly in the case of a short, as compared with the thread pitch, prestressing distance of the elastically prestressable element, in order to be able to set certain axial forces in a specific manner.
The sleeve is furthermore preferably coupled to the moveable part via at least one ball and socket joint. The ball and socket joint makes possible an alignment between the different paths of movement of the sleeve, which acts as a ram, and the moveable part which, for example in the design as a side ventilator window of a motor vehicle, executes a pivoting movement about the B-pillar of the motor vehicle. It has furthermore proven advantageous to provide elastic means between the joint halves of a ball and socket joint, i.e. between the ball head and the ball socket, since even play present in this region increases the tendency to produce noise.